Characterizing Heterogeneous Disorder in Complex Oxides

Structural disorder has a profound effect on a material’s physical properties and can be harnessed for diverse technological applications. For example, the transport properties and radiation response of complex oxides are strongly influenced by the ability of the structure to accommodate disorder while maintaining crystallinity. This research focuses on the structural details of disordered complex oxides which are more intricate that previously believed with the actual atomic arrangements exhibiting distinct ordering across different material length scales (heterogeneous disorder). Disordered spinel (AB2O4) and pyrochlore (A2B2O7) structures are characterized and the atomic arrangements are probed with advanced characterization techniques, such as spallation neutron total scattering with high sensitivity to oxygen. The cation inversion mechanism in spinel structures is shown to be more fundamentally the relative fraction of a locally-ordered structural unit. This behavior, along with similar findings in pyrochlore oxides, is rationalized by straightforward extension of Pauling’s Rules (“The Principles Determining the Structure of Complex Ionic Crystals”). The knowledge gained from this work is directly relevant for several energy and nuclear technologies as fundamental insight into the atomic-scale structure of complex oxides can be used to engineer specific functionalities such as radiation tolerance and ion conduction.